Height Estimation of Soil Erosion in Olive Groves Using a Time-of-Flight Sensor

The olive groves' relevance has historically been ingrained in Mediterranean cultures. Spain stands out as a leading producer worldwide, where olive trees are extensively grown in the Andalusian region. However, despite the importance of this strategic agricultural sector, cultivation through the years has given rise to various crop management practices that have led to disruptive erosion processes. The objective is to measure land erosion in over 100-year-old olive groves considering the 3D reconstructed recent relief of olive tree mounds. A time-of-flight depth sensor, namely, Kinect v2, was employed to 3D model the target areas, i.e., trunk and exposed roots, to determine the height as a surrogate of the difference between the historical and recent relief. In three plots in southern Spain, the height of relic tree mounds was measured in olive trees at the upper and bottom parts to determine soil profile truncation. The results were compared and validated with manual measurements (ground truth values). Olive trees were grouped into high, moderate, and low slope gradient classes. The results showed, in all cases, high consistency in the correlation equations (Pearson's coefficients over 0.95) between the estimated values in the models and the actual values measured in the olive trees. Consequently, these excellent results indicate the potential of this low-budget system for the study of historical erosion. Notably, the Kinect v2 can generate 3D reconstructions of tree mounds at microtopographic scales in outdoor situations that would be challenging for other depth cameras under variable lighting conditions, as found outdoors.